A wide variety of materials have been developed and studied in the search for synthetic replacements for vital internal body parts. Specific study has been focused on prosthetic implant devices used in vascular and cardiac surgery where there is a present need to replace defective or diseased valves and arteries. From this research will come further developments of synthetic replacement devices for other vital body parts.
While flexible, life-like polymeric materials are the most promising for certain internal organs, there are serious problems stemming from the reaction of blood on the polymeric surfaces. This may cause the rupture of red cells and the escape of hemoglobin into the plasma, a condition known as hemolysis, or initiate complex biochemical reactions that lead to thrombosis or clotting.
All polymeric devices, even the so-called non-thrombogenic polymers such as silicone rubber, cause blood clotting in a short period of time. Polytetrafluoroethylene, tetrafluoroethylene, and other polymeric substances are similarly deficient. Whether the polymeric devices are implanted into the body as heart valves, aortas or blood vessels are used as tubing in heart-lung or kidney machines, the blood from the body comes into direct contact with polymers.
It was not until plastic surfaces were treated with heparin, a sulfated mucopolysaccharide found in human lung tissue, blood vessel walls, the liver and small amounts of blood, that the resulting plastics became non-thrombogenic. Several techniques have been developed for chemically binding heparin to surfaces of prosthetic devices. The result has been that heparin-coated polymeric materials effectively retard blood clotting, as shown from both in vitro and in vivo studies, and promise increased use of polymeric devices for use with the body, whether directly implanted or as part of life-generating machine systems.
Equally as serious as the problem of thrombus formation on the prosthetic material is the problem of infection of the prosthetic implant. Prosthetic heart valves and tubular graft materials have displayed vegetative overgrowth caused by bacteria and fungi. These organisms are likely to cover the skirt and strut of the ball and cage type valves as well as the entire surface of the tubular grafts. Infection of the prosthetic implant can lead to disastrous complications including remedial surgery to replace the infected prosthetic implant. What has been needed; therefore, is a non-thrombogenic and anti-microbial composition for application to polymeric devices for use with the body.